1. Field of Invention
This invention relates to methods of synthesizing hydrofluoroolefins. More particularly, the invention relates to catalytic synthesis of 2,3,3,3-tetrafluoro-1-propene.
2. Description of Related Art
The hydrofluoroolefin 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf), which can be used as a low global warming potential (GWP) refrigerant, blowing agent, etc., has been synthesized by the catalytic pyrolysis of methyl chloride and either tetrafluoroethylene or chlorodifluoromethane. For example, U.S. Pat. No. 2,931,840 describes concurrently passing 55 cc/min of MeCl and 110 cc/min CHClF2 through a platinum tube (6 mm×24 in) that is heated to about 800° C. The gaseous product synthesized by this process is scrubbed to remove HCl and dried, but yields only a small amount (14.8 mole %) of 2,3,3,3-tetrafluoropropene. This low yield correlates to almost 90% of the starting material being lost to unimportant byproducts including a significant amount of carbon black, which tends to deactivate the reaction's catalyst.
EP 328148 discloses that fluorine-containing olefins having the formula CH2═CFRf[Rf=(per) halo alkyl group)] can be prepared at low cost and with low toxic waste generation by high-temperature dehydrohalogenation and dehydration of fluoroalcohols such as HOCH2CF2Rf in the presence of H2 gas.
JP 06072925 describes the synthesis of 2,3,3,3-tetrafluoro-1-propanol by reacting tetrafluoroethylene, formaldehyde, and HF in the presence of a TiF4 catalyst and limonene as a polymer inhibitor. The 2,3,3,3-tetrafluoro-1-propanol, in turn, can serve as a starting material to synthesize 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf). The process of JP 06072925 involves feeding a 1:3 (mol/mol) gaseous mixture of HOCH2(CF2)4H and H2 into a tube reactor packed with activated carbon and heated to 500° C. A residence time of 4 seconds yields CH2═CF(CF2)3H at a monomer conversion of 64% and a selectivity of 82%. Although this is a high-yield process, commercial handling of H2 at high temperature is exceptionally hazardous. In addition, the process of JP 06072925 requires a costly on-site generation of H2.
Therefore, there is a need for alternative commercial processes for producing HFO-1234yf that involving more economical and less hazardous starting materials which also result in higher conversion rates and selectivity.